One of the typical explosive charging material especially for bore holes is ANFO (ammonium nitrate-fuel oil explosive), the base material of which is like a dry powder. The explosive end product can be achieved by mixing the dry powder ammonium nitrate with additive material, such as water, fuel oil or special chemicals (later additives). The mixing additionally makes ANFO sticky so to stay better in vertical up holes. Another purpose of increasing the additive is reducing dusting of dry ANFO. Usually this additive is dosed directly to an ANFO tank or right after the tank if special dosing devices are used. However, this method usually results blockages in the ANFO tank and ANFO hoses because of softened half-melted ANFO prill structure. Blockages slow down charging work and due that whole mining cycle.
Also other types of explosive charging materials are used, such as in site sensitized emulsion charging emulsion matrix, which is not explosive material as such, but it is sensitized to emulsion explosive by using dedicated gassing solution which is mixed to matrix. Typically the gassing solution is dosed and mixed in an early stage in process unit and then pumped through water lubricated 20-60 m long charging hose, for example, to the bore hole.
However when gassing solution is mixed in an early stage of emulsion line it means that gassing reaction starts to happen immediately. If for example there 15-30 min shutdown happens during the charging, the emulsion matrix in charging hoses starts to be fully sensitized to emulsion explosive. This creates great danger because detonator and primer are pushed to bore hole by same charging hose which is full of explosive material.
In addition problems relate also to ensuring that the materials used for explosive charging would be introduced in a desired depth in the hole and so that they would not flow to an undesired portion of the hole. The hole may be e.g. an upper hand hole, where the hole is drilled in upward direction, whereupon it must be ensured that the charging materials do not flow away from the hole. Other example is the case of a lower hand hole, where the hole is charged from above and where the charging materials should not enter into the bottom of the hole, or where there is a need to leave an empty portion into the hole and thus ensure that the charging material does not flow into the bottom or into the empty portion of the hole.
Previously mechanical blockages are inserted into the hole before introducing the charging materials. The mechanical blockages, such as fabric bundles are e.g. pushed by long sticks into the hole before charging the hole. This is very cumbersome and slow technique, because at first the mechanical blockage must be inserted into the hole. In addition it is difficult to push by a long stick a mechanical blockage into the hole at a certain depth, because the mechanical blockage tangles easily in the surface of the hole already before suitable location. Especially this is hard with the upper handed holes, where the mechanical blockage must be pushed in upward direction. Furthermore the pushing stick might get broken, whereupon it may be even impossible to get the broken part of the stick away from the hole. Especially all of these steps are time consuming.